Purification of 1,4-butanediol by vacuum distillation with side stream recovery

ABSTRACT

Substantially pure 1,4-butanediol is recovered as a side stream with very low water content by vacuum distillation with water and low boiling impurities taken off overhead and high boiling organic tars and inorganic salts taken off in a liquid bottoms stream.

United States Patent 11 1 1111 3,852,164

Chow et al. Dec. 3, 1974 PURIFICATION OF 1,4-BUTANEDIOL BY [56]References Cited VACUUM DISTILLATION WITH SIDE ED STATES PATENTS STREAMRECOVERY 2,768,214 10/1956 McKinley et a1 260/637 R 7 Inventors; SidneyHsin Huai Chow, 4 1 3,408,265 10/1968 Ward 203/99 Bayon Grove D JamesDaniel 3,530,043 9/1970 :orn et al 503/99 3.692.636 9 1972 uguet 1 O3 99verbsky 103 whlspermg Oaks 3.713.991 1/1973 Thomas 203/99 both ofSeabrook, Tex. 77586 [22] Filed: Mar. 30, 1973 Primary Examiner-WilburL. Bascomb. Jr.

[21] Appi. No.: 346,675

[57] ABSTRACT Substantially pure 1,4-butanediol is recovered as a [52]5% side stream with very low water content by vacuum [51] l t Cl B01 d3/'l0 29/26 distillation with water and low boiling impurities taken[58] "5 99 282/15} off overhead and high boiling organic tars and inor-0 are 60/637 ganic salts taken off in a liquidv bottoms stream.

6 Claims, 1 Drawing Figure l6 v I0 l *lIl 5 f is 5 1 PURIFICATION OF1,4-BUTANEDIOL BY VACUUM DISTILLATION WITH SIDE STREAM RECOVERYBACKGROUND OF THE INVENTION with a minimum of water content for varioususes such 1 as in the manufacture of certain textile fibers. However,conventional multi-stage distillation procedures inherently produce acertain amount of water plus tetrahydrofuran by the breaking down of1,4-butanediol at elevated temperatures. The prior art generally doesnot produce 1,4-butanediol containing less than about 0.2% by weightwater, and frequently the water content is much higher.

One procedure used for the refinement of 1,4- butanediol is discussed inGerman Pat. application OS No. 2,055,892, published May 25, 1972, whichshows the use of several columns in certain combinations. It would bemuch more desirable and economical if a single column process could beused to obtain equivalent or superior results.

US. Pat. No. 2,686,818 Copes, et 211., issued Aug. 17, 1954 describes aprocess for reacting tetrahydrofuran and water in the presence of acatalyst at elevated pressure, and then lowering the pressure in thelower portion of the same column and separating liquid butanediol fromthe remaining tetrahydrofuran and water by distillation. Tetrahydrofuranis generally more costly than butanediol and therefore is not adesirable starting ingredient for the production of butanediol. Also,the operation ofsuch a process, wherein liquid butanediol is separatedfrom the tetrahydrofuran and water in a separate condenser underconditions which do not lead to the maximum purification of thebutanediol, is not the most commercially desirable approach.

SUMMARY OF THE INVENTION The present invention, in certain of itsembodiments, provides a method of recovering 1,4-butanediol containing21 minimum of water from a crude mixture containing l to 20% water andlow boiling organic impurities, 80 to 99% 1,4-butanediol and 0.05 to 5%combined high boiling organic tars and inorganic salts, which methodcomprises passing the crude mixture to a distillation column operatingat subatmospheric pressure and adapted with a reboiler which can beexternal to the column, withdrawing the overhead and returning a portionof the overhead as reflux, passing the bottoms to thereboilen'withdrawing liquid from the bottom of the reboiler, passingvapor from the reboiler to the bottom of the distillation column, andwithdrawing a portion of the vapor passing from the reboiler to thevacuum distillation column as substantially pure 1,4-

butanediol.

Preferably, the absolute pressure in the distillation column is underabout 200 millimeters of mercury and an optimum condition has the top ofthe column-at a pressure of 100 millimeters of mercury. When operatingproperly, the process can produce 1,4-butanediol containing less thanabout 0.1% by weight of water.

DESCRIPTION OF THE DRAWING The sole FIGURE of the drawing is a schematicflow diagram of equipment for operating the process of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventionvutilizes a single distillation O tower to separate 1,4-butanediol fromlow boiling organic impurities and water as overheads and from organictars and inorganic salts as bottoms. Tetrahydrofuran' produced bydecomposition of the 1,4-butanediol exits the column as overhead.

In contrast to prior art processes in which 1,4- butanediol was takenoverhead in the final steps of a multiple distillation process, the1,4-butanediol is not taken overhead in this'process. It has been foundthat crude butanediol, when heated, tends to break down into water plustetrahydrofuran. Also, subatmospheric pressures are used in the presentinvention to permit the use of lower distillation temperatures. This toominimizes the decomposition of the butanediol.- Preferably,

absolute pressures in the distillation column are kept below about 200mm of mercury. A desirable pressure level is about I00 mm Hg at the topof the column and mm Hg at the bottom. 7

Any appropriate conventional type of distillation column could be used.In one preferred embodiment, a tower packed with stainless steel pallrings equivalent to 12 to 14 theoretical plates is used. A tower withactual plates or other types of packing could'also be used in otherpreferred embodiments. v

Turning now to the drawing, it will be seen that the crude butanediolenters through line 1 atower which has an upper half 12 and a lower half1 1. The crude has been heated in preheater 17. Each half, 11 and 12, ispacked with stainless steel pallrings, and the two halves are preferablyseparated, such as by perforated metal plates or screens. Although thehalves can be of about equal size, it also can be preferable for thepacked depth below the inlet to be somewhat larger than that above theinlet, depending on the particular needs to be met.

The overhead stream is taken through overhead condenser 16 by way ofline 7. A vacuum is applied to the system through line 8. Part of theoverhead stream of low boiling organic impurities and water is removedby line 10, and the rest is returned to the upper half 12 of .cess andthe product produced.

From the bottom half 11 of the distillation column, a bottoms stream istaken by line 2 to reboiler 13. A bottom purge is removed by line 4 toeliminate undesirable materials, including a liquid stream of organictars and inorganic salts. Through line 3 a vapor stream of purified1,4-butanediol passes back to bottom half 11 of the distillation column.

Somewhere in the bottom half 11 of the distillation column, line 5removes purified 'l,4-butanediol from the column. The vapor is takenthrough vapor entrainment separator 14 and condenser 15 to side drawproduct line 6. Vacuum is maintained on this part of the system throughanother line shown on condenser 15.

The location of line 5 within bottom half 11 of the distillationcolumnis a matter of choice. Preferably it is at a height lower than thefirst two or three theoretical plates. By positioning line 5 above thevery bottom of the-distillation column, some extra demisting andseparating of high boiling impurities from 1,4-

liquid from the reboiler, passing vapor from the reboiler to the bottomof the distillation column, and withdrawing vapor from the bottomportion of the distillation column as substantially pure l,4butanediol.

bptarredigllsgssured. 2. The process of claim 1 in which a portion ofthe An operating example of th i ti can b n overhead is returned to thedistillation column as rein the following table for a side draw productdesign flux. rate of about 300 pounds per hour. In the table, BAD Theprocess of elaim l ipgliichtheyapor withmeans 1,4-butanediol, and OHmeans overhead. H V drawn from the bottom pgrtiqr f: goi- FLOWSHEETCOMPOSITION WEIGHT PERCENT Stream Stream Temp. Pressure Densit'y LowHigh Tar Description No. lbs./hr. C. mm Hg lbs./cu.ft. BAD H2O BoilersBoilers & Salts Column Feed I 500 I30 110 58.02 93.09 5.0 0.17 0.24 1.50Liquid [0 Reboiler 2 927.8 l77.8 129.2 55.12 Vapor from Reboiler 3 842.4180.0 l3l.4 0.026 Bottom Purge 4 85.4 l80.0 l3l.4 57.03 90.59 0.63 8.78Side Draw Vapor 5 300 177.8 [29.2 0.026 I Side Draw Product 6 300 50.0760.0 63.4 99.66 0.07 0.05 0.22 Vapor m O.H. 7 368.6 152.0 90.0 0.012Condenser O.H. condenser Vent 8 l3 68.0 90.0 0.005 2.77 95.85 1.38Reflux 9 254 68.0 90.0 60.33 0.H. Take Off l0 101.6 68.0 90.0 60.3337.35 12.14 0.51

. umn is a portion of the vapor produped by the reboiler. What"iic-l-qlmsgfil 4. The process of claim 1 in which the distillation coi-A Process of recoveflng 1,4-bl1tafled10l a q g umn is operated at anabsolute pressure under about a minimum of water from a crude mIxturecontaining, 200 illi f mercury y weight, to 20% Water P boiling Organic5. The process of claim 1 in which the distillation col- P 80 to i i to5% umn is operated at an absolute pressure of about 100 combined hIghboilmg organic tars and Inorgamc salts, il i f mercury which methodComprises P g the Crude mixturei to 6. The process of claim 1 in whichthe recovered 1,4- distllatlon wlumn operatmg at E 'fip P butanediolcontains less than about 0.1% by weight of sure and adapted with areboiler, wIthclrawIng the overwater head, pa iii the b ttbms t0. th eqiettwitliqiauivg ii i.

1. A PROCESS FOR RECOVERING 1,4-BUTANEDIOL CONTAINING A MINIMUM OF WATERFROM A CRUDE MIXTURE CONTAINING,BY WEIGHT, 1 TO 20% WATER PLUS LOWBOILING ORGANIC IMPURITIES, 80 TO 99% 1,4-BUTANEDIOL, AND 0.05 TO 5%COMBINED HIGH BOILING ORGANIC TARS AND INORGANIC SALTS, WHICH METHODCOMPRISES PAASSING THE CRUDE MIXTURE TO A DISTILLATION COLUMN OPERATINGAT SUBATMOSPHERIC PRESSURE AND ADAPTED WITH A REBOILER, WITHDRAWING THEOVERHEAD, PASSING THE BOTTOMS TO THE REBOILER, WITHDRAWING LIQUID FROMTHE REBOILER, PASSING VAPOR FROM THE REBOILER TO THE BOTTOM OF THEDISTILLATION COLUMN,AND WITH-
 2. The process of claim 1 in which aportion of the overhead is returned to the distillation column asreflux.
 3. The process of claim 1 in which the vapor withdrawn from thebottom portion of the distillation column is a portion of the vaporproduced by the reboiler.
 4. The process of claim 1 in which thedistillation column is operated at an absolute pressure under about 200millimeters of mercury.
 5. The process of claim 1 in which thedistillation column is operated at an absolute pressure of about 100millimeters of mercury.
 6. The process of claim 1 in which the recovered1,4-butanediol contains less than about 0.1% by weight of water.